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NFPA Exam CFPS Topic 6 Question 12 Discussion

Actual exam question for NFPA's CFPS exam
Question #: 12
Topic #: 6
[All CFPS Questions]

The primary mechanism by which carbon dioxide extinguishes fire is

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Suggested Answer: C

The primary mechanism by which carbon dioxide extinguishes fire is smothering, or displacing the oxygen that the fire needs to sustain combustion. Carbon dioxide is a gas that is heavier than air, so when it is released from the extinguisher, it forms a blanket over the fire and pushes away the oxygen. Without oxygen, the fire cannot continue to burn and is extinguished1234

Cooling is a secondary mechanism by which carbon dioxide extinguishes fire. Carbon dioxide is stored as a liquid under high pressure in the extinguisher, and when it is released, it expands rapidly and cools down. The cold gas absorbs heat from the fire and lowers the temperature of the fuel below its ignition point. However, cooling is not the main effect of carbon dioxide, as it is less effective than water in reducing the heat of the fire1234

Saponification and chemical inhibition are not mechanisms by which carbon dioxide extinguishes fire. Saponification is a process by which wet chemical agents react with fats and oils to form a soapy foam that seals the surface of the fire and prevents re-ignition. Chemical inhibition is a process by which dry chemical agents interfere with the chemical chain reaction of the fire and stop the production of free radicals that propagate the combustion. These mechanisms are used by other types of fire extinguishers, such as Class K and Class D extinguishers, respectively1234


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by Elza at Jul 06, 2025, 11:35 AM

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Tennie
1 days ago
I think the answer is C) smothering.
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Nan
8 days ago
A) cooling. Wait, is that even a thing? Someone needs to fire the exam writer, pun intended.
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Brock
10 days ago
D) chemical inhibition. Gotta love those fancy-sounding scientific terms, am I right?
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Carmela
11 days ago
C) smothering. That's the one! Carbon dioxide deprives the fire of oxygen, simple as that.
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